Driving balance-wheels more particularly applicable to timing instruments



May 30, 19 M. J. LAVET ET AL DRIVING BALANCE-WHEELS MORE PARTICULARLY APPLICABLE TO TIMING INSTRUMENTS 3 Sheets-Sheet 1 Filed July 25, 1957 May 30, 1961 LAVET ET AL 2,986,683

DRIVING BALANCE-WHEELS MORE PARTICULARLY APPLICABLE TO TIMING INSTRUMENTS Filed July 25, 1957 5 Sheets-Sheet 2 y 30, 1961 M J. LAVET ET AL 2,986,683

ORE PARTICULARLY DRIVING EALANCE- EELS M APPLICABLE TIMING INSTRUMENTS Filed July 25, 1957 3 Sheets-Sheet IS United States Patent i DRIVING BALANCE-WHEELS MORE PARTICU- LARLig APPLICABLE TO TIMING INSTRU- MENT Marius Jean Lavet and Jacques Jean Gustave Dietsch,

Paris, France, assignors to Societe Anonyme Etablissements Leon Hatot, Paris, France, a corporation of France Filed July 23, 1957, Ser. No. 673,649

Claims priority, application France July 26, 1956 6 Claims. (Cl. 318132) The present invention has for its object improvements in balance-wheels and driving devices of the alternating motion type, actuated by electro-magnetic impulses.

These improvements are especially applicable to portable apparatus intended to give the time, to measure intervals of time, to emit periodically signals or control currents, etc.

The invention is more particularly related to the known type of isochronous mechanical oscillator formed by a balanced mass mounted on a pivot and associated with a spiral or helicoidal spring. This mass oscillates with a large amplitude like the balance-wheels of the usual kinds of watches. The maximum amplitude or are of oscillation may amount to 270 on each side of the position of rest of the balance-wheel (which position is known as the dead point or position of equilibrium).

In a prior clock power device the present applicants have constructed a driving balance-wheel which comprises two permanent magnets moving in the vicinity of a fixed coil intended to produce driving impulses by means of a junction transistor and an electro-magnet. Tests have shown that the system in question can operate but the elficiency of the electro-magnetic members is however low and it becomes necessary to employ a high amplification of the current induced in the impulse coil. Under these conditions, the electrical consumption of the apparatus is relatively high and its operation necessitates a battery of a number of elements, which is not admissible in the case of many industrial applications.

It has also been found that it was not possible to manufacture economically the perforated magnets with the magnetic substances of very high quality which are very diflicult to work, and the cost of which is very high. The shapes of these magnets are complicated and they require too large quantities of material, a considerable part of which is lost.

The present invention overcomes these serious drawbacks and enables the manufacture to be simplified. It is possible to greatly reduce the quantities of costly materials required for the construction of magnets of high quality, extremely fine enamelled copper wires. The operation of the balance-wheel is effected with great reliability for more than one year when using a single dry battery element of very small size.

These results have been obtained by the new and special features of construction which reduce the electrical losses and ensure with greater effectiveness the use of the magnetic flux produced by magnets of small size and simple shapes.

The invention has also for its object the construction of an improved system of oscillating motor which enables chronometric transmitters of very high precision to be produced and also clockwork movements of very simple manufacture, particularly suitable for apartment clocks and automobile clocks which it is necessary to produce in very large quantities at very low prices.

These and other objects and special features of the present invention will be brought out more clearly from Patented May 30, 1961 lCe the detailed description which follows with reference to the accompanying drawings, in which:

Fig.1 is a cross-section taken along a vertical plane passing through the axis of a circular balance-wheel comprising two pairs of alternate magnetic poles surrounding two flat superposed windings.

Fig. 2 shows the same system seen in cross-section along the horizontal plane defined by the line 2-2 of Fig. 1. This Fig. 2 also shows in the form of a diagram, the accessory members and electrical connections which enable the isochronous oscillation of the balance-wheel of Fig. 1 to be maintained.

Fig. 3 is a further transverse cross-section of the balance-wheel taken along the line 3-3 of Fig. 2.

Figs. 4 and 5 show separately the magnetic and nonmagnetic pieces which form part of the construction of the mass of the balance-wheel shown in Fig. 1.

Figs. 6 to 9 show a first alternative form of construction of the system of driving balance-wheel of Figs. 1 to 5.

Fig. 10 is a diagram which shows the application of the system of Figs. 1 to 5 or Figs. 6 to 9 to the distribution of periodic signals intended to actuate a receiving clock at a distance.

Figs. 11 to 13 show a driving balance-wheel similar to the device shown in Fig. 6, but which comprises two fiat juxtaposed coils.

Figs. 14 and 15 show an alternative form of construction of the system of Figs. 1 to 5, which consists in dividing the two windings between three parallel magnets forming the body of the balance-wheel.

Figs. 16 and 17 show two particular positions of the four moving magnetic poles which act by electro-magnetic induction on the operating coil coupled to the input terminals of the amplifier.

Fig. 18 is a diagram indicating as a function of time, the form of the current impulses delivered by the amplifier (which currents pass through the driving coil and produce the electro-magnetic forces which actuate the balance-wheel) In all the drawings, the improved apparatus in accordance with the invention is shown by sketches which are partly diagrammatic. In order to simplify the drawings, the accessory parts such as certain supports and frames have not been shown. The air gaps and the thicknesses of very thin pieces have been shown greater than in their true proportions.

The main members, which form part of the construction of all the types, are designated by the reference letters given below:

A A permanent magnets of the balance-wheel;

N--N: north polar zones;

S-S: south-polar regions;

BC: control or actuating coil in which is developed by electro-magnetic induction the input current which makes the transistor amplifier 51 conductive;

1': input current or signal;

1: output current which produces the driving impulses;

BE: driving coil through which passes the output current acting on the permanent magnets of the balance-wheel;

A junction transistor 51 P.N.P. (shown by way of example as a crystal amplifier);

A spiral spring 52 associated with the body of the balance-wheel enabling a constant period of oscillation T to be obtained;

An insulating support 53 for the coils BC and BE;

G: source of energy of continuous current or alternating current rectified by an electric valve or a diode.

The devices forming the object of the invention have the following characteristics, all of which have proved to be necessary in obtaining the objects desired:

(1) The stationary coils BC and BE are very flat; they are formed by very close windings of very fine enamelled copper wire and the insulating cheeks of these coils are extremely thin (for example the wires are simply held in position by being stuck together with an appropriate insulatingvarnish); the magnetic field poles pass very close to the coils.

(2) The coils are not provided with ferro-magnetic cores; they are hollow or are provided with cores of insulating material.

(3) The planes of the turns are normal to the axis of rotation of the balance-wheel.

(4) The dimensions of the turns are relatively small with respect to the total diameter of the balance-wheel (for example, the largest dimension of the coil is less than the maximum radius of the oscillating mass).

(5) When the balance-wheel passes through its position of equilibrium at its maximum angular speed, the two sides of the coil BC cut the lines of force forming two inducing fluxes which are very concentrated and of very high density. These active fluxes are parallel to the axis of the balance-wheel and are opposite in direction.

(6) The lateral active parts of the coils BC and BE are no longer traversed by magnetic fluxes when the balance-wheel has rotated through an angle less than 90 on each side of the position of equilibrium; under these conditions, the electro-magnetic action applied to the oscillating mass is entirely annulled when the balancewheel is considerabaly displaced from its equilibrium position. This property is retained even if the driving coil BE has passing through it continuously a small electric current due to the fact that the transistor may have a small conductivity in the interval between impulses (see the curve of Fig. 18).

Referring now to Figs. 1 to 5, there is shown a balancewheel of a portable clockwork instrument provided with two small circular fly-wheels rigidly fixed to the central pivotal spindle 30. On this spindle is fixed the inner extremity of a spiral spring 52. The spindle 30 is preferably mounted vertically.

The outer extremity of the spiral spring is fixed to the rod 31 carried by the frame.

The fly-wheels are formed by two dished members 32 and 33 of non-magnetic metal, rigidly fixed to a central hub 34. In the interior of the dished members are fixed (by gluing or soldering) the parts 35, 36, 37 and 38 which are shown separately in Figs. 4 and 5. These parts form two co-axial rings arranged as shown in Figs. 2 and 3.

The small parts 36 and 38 are very powerful two-pole magnets in the form of portions of a ring, the angle a (see Fig. 4) being about 50. These magnets are arranged to face each other with a very small air gap or spacing d, the poles of opposite sign being disposed opposite each other as shown in Figs. 3 and 4.

The slotted rings 35 and 37 are made of a non-magnetic material such as brass.

The arrangements which have just been described enable very intense magnetic fluxes and to be created between the polar extremities of the magnets 36 and 38, that is to say in the regions indicated by arrows in Fig. 3. It can be seen that these two active fluxes are parallel to the axis of rotation 0-0, but that their directions are opposite.

It has been found that it is a great advantage to form the small magnets 36 and 38 of an anisotropic material which has at the same time a high magnetic induction (Bz) and a high coercive field (Hc). Magnets of this kind can be obtained by known metallurgical methods (thermal and magnetic treatments combined) which give to the material a preferential direction of strong magnetisation in the direction of the diametral line 39 shown in Figs. 4 and 5. The external lines of force pass through the air between the adjacent N and S poles, as shown in Fig. 3.

In order to produce the small magnets 36 and 38, var ious known materials can be used with advantage, such as Ticonal X described in the publication Philips Research Reports 11, 489490, '1956 (article by A. I. Luteijn and K. J. de Vos). In the case of clockwork instruments of small size, it is possible to use the new substances with very high magnetic density, such as the platinum-cobalt and manganese-bismuth alloys, and also magnets made from ultra-fine powders. These materials are very expensive, but the method of construction shown in Figs. 1 to 5 reduces to a minimum the quantities of material to be used. In addition, the simple shape of the magnets 36 and 38 permits an economic production of interchangeable parts by moulding and sintering ferro-magnetic powders selected from those which give the best results.

Between the movable rings are arranged two coils BC and BE superposed as shown in Figs. 1 and 2. These coils are embedded and glued into a flat support 53 of insulating material. They have a large number of turns (for example each coil comprises more than 1500 turns).

Fig. 2 shows the balance-wheel in the position of rest (known in the watch-making industry as the position of equilibrium or dead center). It can be seen that for each coil, bundles of conductors are located approximately along the radii of the balance-wheel passing through the poles N and S of each magnet. The bundles considered are respectively located in extremely high density magnetic fields, the directions of which are indicated by the arrows in Fig. 3 (arrows parallel to the axis 0-0 of the balance-wheel). The portions of the copper wire of the coil BC located in front of the N and S poles of the magnets 36 and 38 constitute the active conductors in which are induced electro-motive forces when the oscillating balance-wheel passes in the vicinity of its position of equilibrium at its maximum angular speed.

When the active conductors cut the lines of force between the poles of the moving magnets, a diiference of potential is produced across the terminals of the control coil BC and this intermittent electric potential generates short input currents i which act on the transistor 51.

The crystals of the transistor 51 become conductive and permit the passage of an output current I which passes into the driving or sustaining coil BE. The connections of this coil are chosen in such manner that the electromagnetic forces generated by it act in the direction of the movement and supply energy to the balance-wheel in the form of short impulses and sustained oscillation takes place in the direction of the two arrows f f Experience has shown that the parameters of construction can easily be determined so as to ensure that, by means of a source G of very low voltage (1.3 volts for example) the balance-wheel oscillates with a very large amplitude (270 approximately) on each side of its position of equilibrium (see Fig. 2). The balance-wheel shown in Fig. 1 can thus operate with the aid of a single element of a dry battery or accumulator.

It will be noted that, when the balance-wheel moves away by more than from the position shown in Fig. 2, the inducing fluxes and 11 produced by the moving magnets move away from the coils BC and BE. In consequence, the input current i falls to zero and the resistance of the crystals of the transistor 51 becomes a maximum. The output current I becomes very small and, as the conductors of BB do not cut any line of force, the electro-magnetic actions are Zero. This property enables the isochronism of the oscillations to be ensured in spite of the small variations of the arc of oscillation.

The self-maintained balance-wheel of Figs. 1 to 5 enables various types of independent clockwork instruments to be constructed. For example, it may actuate hands through intermittent transmission mechanism not shown.

The balance-wheel may also be provided with a finger 39 which causes the first ratchet wheel 40 of a chronometric counter to advance step-by-step (a well-known systern of transmission).

A roller 41 (or an equivalent magnetic device) facilitates the tooth-by-tooth progression of the ratchet wheel 40 (see Fig. 2).

The self-maintained balance-wheel may be employed without mechanical transmission and enclosed in a small movable fluid-tight casing provided with connection plugs. In order to be able to use it as a signal transmitter, a periodic potential it may be taken from the terminals of the coils BM. This potential applied to the input of an auxiliary amplifier enables very large emissions to be produced, capable in particular of actuating receiving clockwork apparatus, following various methods which are known per se.

The synchronisation of secondary clocks or the control of receiving clocks may also be effected by the intermediary of photo-electric relays constructed in accordance with various known techniques.

Tests have shown that the choice of the spiral spring 52 and the care given to the manufacture of the pivots enable a very good regularity of oscillatory movement to be obtained, especially when a source of energy G, having a substantially constant potential is used (which is the case with mercury dry cells giving small currents). The stability of the period during very long durations of operation may be still further improved by reducing the friction of the pivots O and O, and this result is readily obtainable by the use of footsteps and bearings of the magnetic repulsion type (a device already applied to the balance-wheels of clocks).

An alternative form of construction of the driving balance-wheel of Figs. 1 to 5 is shown in Figs. 6 to 9. Two portions of this balance-wheel are obtained by cutting out or moulding under pressure thin pieces 42 and 43, the shape of which can be seen from the plan View of Fig. 7 and in the perspective View of Fig. 8.

The pieces 42 and 43 are made of materials having a high coercive field, capable of retaining a strong magnetisation, although the internal lines of force are short and straight. There may be used for example the alloys known as Cunico and Cunife and Vicolloy together with the anisotropic materials recently prepared, which retain a very high magnetic energy. Only the oval parts or end portions marked A and A in Fig. 9 are magnetised to saturation; the directions of the internal lines of force are indicated by arrows on the drawing in Fig. 8. The opposite symmetrical enlarged ends marked are left neutral and do not produce any external magnetic flux. In these neutral end portions, the small Weiss fields should remain in disorder and should neutralise each other; in consequence, everything takes place as if the neutral end portions were made of non-magnetic materials.

The active lines of force are created between the magnets A and A and they form a first magnetic flux (1) between the poles N and S and a second flux 5 of opposite direction between N and S These fluxes and 5 are parallel to the axis of rotation OO and they are relatively close together, the average flux lines being spaced apart at an approximate distance or interval D as shown in the drawing in the various figures.

The flat fixed coils BC and BE are placed as shown in Fig. 6 (elevation) in Fig. 7 (plan) and in Fig. 9 (partial cross-section along the line 99 of Fig. 7). These coils are embedded in the insulating plate 53 and they are placed between the magnets A and A when the balance-wheel passes through its position of equilibrium, as shown in Fig. 7. This figure also shows the electrical diagram in which there will be observed: impedances Z and Z intended to modify the current i required to periodically free the output circuit of transistor 51, and a capacity C intended to prevent the continuation of a current of high frequency due to the eflect of direct coupling between the Winding BC and BE. The parts Z and C are not absolutely essential, but it has been found that they enable the consumption of current to be substantially reduced.

It can be seen that the balance-wheel of Figs. 6 to 9 has the main characteristic features of the system of 6 Figs. 1 to 5; it is therefore not necessary to describe its operation.

The apparatus of Figs. 1 to 5 also enables a counting train to be actuated directly (for example by means of a finger moving a lever and acting on a ratchet wheel through a pawl 01' through a driving escapement).

An important special feature of the device shown in Fig. 6 is the auxiliary fly-wheel 44, the construction of which is similar to that of the compensated balancewheels of marine chronometers. As shown in Fig. 6, the fly-wheel 44 comprises two masses 45 and 45 fixed on curved bi-metallic strips 46 and 46. These strips are formed by two metals the coefiicients of expansion of which are different; they become deformed when the ambient temperature varies. The influence on the period of oscillation is easily regulated by moving the masses 45 and 45. In this way, changes of period can be avoided arising for various causes such as variations in the gain of the amplifier 51 when the temperature varies.

A further method of thermal compensation is obtained from the possibility of introducing in the circuit of BC resistances Z and Z composed of semi-conductors which are strongly affected by temperature. The circuit elements Z and Z thus provide new technical means adapted to be combined with those which are currently applied in mechanical clock construction. Tests have shown that the deformable fly-Wheel 44 is very convenient in use to neutralise rapidly the influence of temperature on balance-wheels actuated by the medium of germanium transistors. In fact, it is only necessary to observe the effects of changes of temperature by means of a vibrograph supplied by the periodic potential it (see diagram of Fig. 7). In accordance with these findings, the masses 45 can be suitably displaced.

Fig. 10 is a basic diagram which shows the use as a mother clock of the apparatus of Fig. 7 self-maintained by means of the transistors 51. The terminals of a second transistor 51 are interposed in the output circuit of transistor 51 and a control circuit is formed comprising an auxiliary source of energy G and the winding 47 of a clockwork receiver 48.

Many changes or modifications may be made to the devices described above without thereby departing from the spirit of the invention. In paiticular, the construction of balance-wheels intended for apparatus in everyday use can be simplified, since these apparatus do not require any great precision but they must be manufactured at a low price.

For example, instead of superposing two very flat coils which require very fine costly and fragile wire, two windings of thicker wire can be juxtaposed. This alternative form is shown in Figs. 11 and 12.

It can be seen from these figures that the general principles employed have not changed and that the improvements of the invention are again applied to a great extent. The oscillating members should be magnetised on one side only of the axis is shown by the arrows. These parts can be produced by molding under pressure powders of ceramic materials such as those termed Ferrox dure II and Indo-x V. The insulating support IS of the coils can contain the transistor TR, which facilitates the electrical connections.

The balance-wheel can control hands by means of the device shown in Fig. 11 (this transmission being already well known and employed in various electrical automobile clocks).

Instead of using a balance-wheel carrying two magnets in opposition, three superposed magnets A A and A may be used as shown in Figs. 14 and 15, which enables the coil BC to be placed between A and A and the coil BE between A and A In this way, the inductive magnetic fluxes passing through the sides of the coils is increased, which enables the electrical consumption to be reduced.

In order to reduce the cost of the balance-wheel shown in Fig. 15, a central and relatively thick magnet A of moulded material will preferably be employed, the thin magnets A and A being produced by cutting out from steel sheet.

The balance-wheel can rotate the ratchet wheel 40 (of steel) step-by-step by means of the finger 39, the ratchet being attracted into its appropriate successive positions by the small magnet 49.

The balance-wheel of Figs. 12 and 15 are suitable for automobile clocks supplied from the accumulator battery on board. In this case, it may be useful to make the voltage acting on the coil BE uniform. For that purpose, various known devices may be used, for example that which is shown diagrammatically on the right hand side of Fig. 14. This circuit comprises a resistance R and a non-linear semi-conductor VDR, the resistance of which falls automatically when the voltage U of the battery rises. It can be seen that when the voltage U rises to an excessive value, the current I in the resistance R tends to increase, which increases the voltage drop in this resistance. This loss of voltage limits the increase of the driving impulses and regularises the amplitude of the balance-wheel.

Figs. 16 and 17 and the curves shown in Figs. 18 enable the conditions of operation of all the apparatus previously described to be analysed.

The curve (2) drawn in heavy lines in Fig. 18 shows the variation as a function of time of the current i which passes through the driving coil BE. This curve (2) reproduces the shape of the line of light appears on the screen of a cathode ray oscilloscope which serves to control the output current i of the amplifier 51.

The points marked 0, t t correspond to the passages of the balance-wheel through its position of equilibrium. The curve (1) drawn in dotted lines is a smusoidal curve which shows the variations of the angle of rotation of the balance-wheel as a function of time.

It is found that at the instants O and t the output circuit of the amplifier is sharply opened, which permits the passage of the maximum output current I. This phenomenon takes place when the magnets A and A of the balance-wheel are moved at maximum speed, surrounding the coil BC as shown in Fig. 16. After a small angular travel, the magnets move away from the coil BC and the current i falls to a very low value i This current i does not produce any electro-magnetic force since the flux is nil.

On the return of the balance-wheel in the opposite direction of h, the output circuit is opened twice in succession in the vicinity of the instant 1 This results in two successive driving impulses which take place when the magnets A and A pass through the positions indicated in dotted lines and in full lines in Fig. 17. These two impulses are very close together and are equivalent to a single impulse taking place at the dead center and it follows from the theory of operation of clocks that the form of the current i is particularly well suited to the production of clockwork instruments operating with great precision. The conditions of maintainance of the balancewheels are those which are obtained with the best escapements used for the production of the usual types of chronometer.

What is claimed is:

1. In a portable time-keeping apparatus, in combination, a balance wheel comprising, at least two like spaced, rotatably mounted, jointly oscillatable symmetrical members each having a magnetic portion oscillatable in equal opposite directions from a predetermined median position corresponding to a position of equilibrium, means providing a pivotal axis about which said members oscillate and relative to which the magnetic portions are concentrically disposed, said members being disposed axially spaced on said pivotal axis, said magnetic portions having spaced north and south poles radially equidistant from the pivotal axis and disposed within a sector defining an angle of no greater than ninety degrees at said axis, the magnetic portions being disposed in operation confronting each other defining an air gap between them and the north pole of one portion confronting a south pole of the other portion to form in operation a field of magnetic lines of force having lines of force in said gap substantially parallel to the pivotal axis, a stationary driving coil and a stationary control coil disposed to cut said magnetic lines of force in the gap when the magnetic portions are disposed in said position of equilibrium, a transistor connected to the control coil and rendered conductive thereby in operation by a periodic voltage generated in the control coil and whose peak value corresponds to intervals of time corresponding substantially to intervals in the oscillations of the magnetic portions when they travel past the position of equilibrium and are traveling at their maximum angular speed during an oscillation, a source of power connected to the transistor, connections between the transistor and the driving coil to produce a momentary flow of current in said driving coil when said transistor is rendered conductive and in a direction for continuing the oscillations of said magnetic portions.

2. In a portable time-keeping apparatus, in combination, a balance-wheel comprising at least two like spaced, rotatably mounted, jointly oscillatable annular members each having a sector thereof forming a magnetic portion oscillatable in equal opposite directions from a predetermined median position corresponding to a position of equilibrium, means providing a pivotal axis about which said members oscillate and relative to which the magnetic portions are concentrically disposed said members being disposed axially spaced on said pivotal axis, said magnetic portions having spaced north and south poles radially equidistant from the pivotal axis and disposed within a sector defining an angle of no greater than ninety degrees at said axis, the magnetic portions being disposed in operation confronting each other defining an air gap between them and the north pole of one portion confronting a south pole of the other portion to form in operation a field of magnetic lines of force having lines of force in said gap substantially parallel to the pivotal axis, a stationary driving coil and a stationary control coil disposed to cut said magnetic lines of force in the gap when the magnetic portions are disposed in said position of equilibrium, a transistor connected to the control coil and rendered conductive thereby by periodic voltage generated in the control coil and whose peak value corresponds to intervals of time corresponding substantially to intervals in the oscillations of the magnetic portions when they travel past the position of equilibrium and are traveling at their maximum angular speed during an oscillation, a source of power connected to the transistor, connections between the transistor and the driving coil to produce a momentary flow of current in said driving coil when said transistor is rendered conductive and in a direction for continuing the oscillations of said magnetic portions and to oscillate said members at an angle greater than 45 in each opposite direction from said position of equilibrium.

3. In a portable time-keeping apparatus in combination, a balance wheel comprising at least two like spaced, rotatably mounted, jointly oscillatable elongated symmetrical flat members each having end portion formed as a magnetic portion oscillatable in equal opposite directions from a predetermined median position corresponding to a position of equilibrium, means providing a pivota1 axis about which said members oscillate and relative to which the magnetic portions are concentrically disposed, said members being disposed axially on said pivota1 axis, said magnetic portions having spaced north and south poles radially equidistant from the pivotal axis and disposed within a sector defining an angle of no greater than ninety degrees at said axis, the magnetic portions being disposed in operation confronting each other defining an air gap between them and the north pole of one portion confronting a south pole of the other portron to form in operation a field of magnetic lines of force having lines of force in said gap substantially parallel to the pivotal axis, a stationary driving coil and a stationary control coil disposed to out said magnetic lines of force in the gap when the magnetic portions are disposed in said position of equilibrium, a transistor connected to the control coil and rendered conductive there by by a periodic voltage generated in the control coil and whose peak value corresponds to intervals of time corresponding substantially to intervals in the oscillations of the magnetic portions when they travel past the position of equilibrium and are traveling at their maximum angular speed during an oscillation, a source of power connected to the transistor, connections between the transistor and the driving coil to produce a momentary flow of current in said driving coil when said transistor is rendered conductive and in a direction for continuing the oscillations of said magnetic portions and to oscillate said members at an angle greater than 45 in each opposite direction from said position of equilibrium.

4. *In a portable time-keeping apparatus in combination, a balance wheel comprising at least two like spaced, rotatably mounted, jointly oscillatable symmetrical members each having a magnetic portion oscillatable in equal opposite directions from a predetermined median position corresponding to a position of equilibrium, means providing a pivotal axis about which said members oscillate and relative to which the magnetic portions are concentrically disposed said members being disposed axially spaced on said pivotal axis, said magnetic portions having spaced north and south poles radially equidistant from the pivotal axis and disposed within a sector defining an angle of no greater than ninety degrees at said axis, the magnetic portions being disposed in operation confronting each other defining an air gap between them and north pole of one portion confronting a south pole of the other portion to form in operation a field of magnetic lines of force having lines of force in said gap substantially parallel to the pivotal axis, a stationary driving coil and a stationary control coil disposed radially of the driving coil to cut said magnetic lines of force in the gap when the magnetic portions are disposed in said position of equilibrium, a transistor connected to the control coil and rendered conductive thereby by a periodic voltage generated in the control coil and whose peak value corresponds to intervals of time corresponding substantially to intervals in the oscillations of the magnetic portions when they travel past the position of equilibrium and are traveling at their maximum angular speed during an oscillation, a source of power connected to the transistor connections between the transistor and the driving coil to produce a momentary flow of current in said driving coil when said transistor is rendered conductive and in a direction for continuing the oscillations of said magnetic portions and to oscillate said members at an angle greater than 45 in each opposite direction from said position of equilibrium.

5. In a portable time-keeping apparatus in combinatiou, a balance-wheel comprising three like spaced, rotatably mounted, jointly oscillatable elongated, symmetrical fiat members each having an end portion formed as a magnetic portion oscillatable in equal opposite directions from a predetermined median position corresponding to a position of equilibrium, means providing a pivotal axis about which said members oscillate and relative to which the magnetic portions are concentrically disposed said members being spaced axially on each axis, said magnetic portions having spaced north and south poles radially equidistant from the pivotal axis and disposed within a sector defining an angle of no greater than ninety degrees at said axis, the magnetic portions being disposed in operation confronting each other defining two air gaps between them and the north pole of one portion confronting a south pole of the other portion to form in operation a field of magnetic lines of force having lines of force in said gaps substantially parallel to the pivotal axis, a stationary driving coil and a stationary coil disposed axially spaced and radially relative to said axis, to cut said magnetic lines of force in the gaps when the magnetic portions are disposed in said position of equilibrium a transistor connected to the control coil and rendered substantially by periodic voltage generated in the control coil and whose peak value corresponds to intervals of time corresponding substantially to intervals in the oscillations of the magnetic portions past the position of equilibrium and are traveling at their maximum angular speed during an oscillation, a source of power connected to the transistor, connections between the transistor and the driving coil to produce a momentary flow of current in said driving coil when said transistor is rendered conductive and in a direction for continuing the oscillations of said magnetic portions and to oscillate said members at an angle greater than 45 in each opposite direction from said position of equilibrium.

6. A portable time-keeping apparatus according to claim 5, in which said pivotal axis is vertically disposed and the three symmetrical members forming the balancewheel are disposed in parallel relationship, and normal to said pivotal axis, and in which the control coil is disposed between an upper magnetic portion and a central magnetic portion, and the driving coil being disposed between the central magnetic portion and a lower magnetic portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,652,504 Pinter Sept. 15, 1953 2,769,946 Brailsford Nov. 6, 1956 FOREIGN PATENTS 501,713 France Feb. 4, 1920 523,885 France Apr. 30, 1921 746,465 Great Britain Mar. 14, 1956 986,536 France Mar. 28, 1951 1,092,411 France Nov. 10, 1954 

